Implantable device lead including a distal electrode assembly with a coiled component

ABSTRACT

A medical device lead includes an insulative body having a proximal region with a proximal end, and a distal region with a distal end. The medical device lead also includes a connector coupled to the proximal end of the insulative body of the lead to electrically and mechanically connect the lead to an implantable pulse generator. The medical device lead further includes a conductor extending through the insulative body with a proximal end electrically connected to the connector. A distal electrode assembly at a distal end of the insulative body includes a proximal portion electrically coupled to a distal end of the conductor, a distal portion, and an intermediate portion. The intermediate portion comprises a coiled element electrically connecting the proximal portion and distal portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Provisional Application No.61/654,446, filed Jun. 1, 2012, which is herein incorporated byreference in its entirety.

TECHNICAL FIELD

The present disclosure relates to implantable medical devices. Moreparticularly, the present disclosure relates to a distal lead electrodeassembly including a coiled electrode component and/or an electricallyisolated moveable fixation helix.

BACKGROUND

Magnetic resonance imaging (MRI) is a non-invasive imaging procedurethat utilizes nuclear magnetic resonance techniques to render imageswithin a patient's body. Typically, MRI systems employ the use of amagnetic coil having a magnetic field strength of between about 0.2 to 3Teslas (T). During the procedure, the body tissue is briefly exposed toradio frequency (RF) pulses of electromagnetic energy in a planeperpendicular to the magnetic field. The resultant electromagneticenergy from these pulses can be used to image the body tissue bymeasuring the relaxation properties of the excited atomic nuclei in thetissue.

During imaging, the electromagnetic radiation produced by the MRI systemmay be picked up by implantable device leads used in implantable medicaldevices such as pacemakers or cardiac defibrillators. This energy may betransferred through the lead to the electrode in contact with thetissue, which may lead to elevated temperatures at the point of contact.The degree of tissue heating is typically related to factors such as thelength of the lead, the conductivity or impedance of the lead, and thesurface area of the lead electrodes. Exposure to a magnetic field mayalso induce an undesired voltage on the lead. Further, in some cases,certain components of the lead can cause image artifacts in the magneticresonance image.

SUMMARY

Disclosed herein are various embodiments of a medical device leadincluding a distal lead electrode assembly including a coiled electrodecomponent, as well as medical device systems including such electrodeassemblies.

In Example 1, a medical device lead includes an insulative body having aproximal region with a proximal end, and a distal region with a distalend. The medical device lead also includes a connector coupled to theproximal end of the insulative body of the lead to electrically andmechanically connect the lead to an implantable pulse generator. Themedical device lead further includes a conductor extending through theinsulative body with a proximal end electrically connected to theconnector. A distal electrode assembly at a distal end of the insulativebody includes a proximal portion electrically coupled to a distal end ofthe conductor, a distal portion, and an intermediate portion. Theintermediate portion comprises a coiled element electrically connectingthe proximal portion and distal portion.

In Example 2, the medical device lead according to Example 1, whereinthe distal portion of the distal electrode assembly includes a contactelectrode having an outer diameter larger than outer diameters of theproximal portion and intermediate portion, and wherein the insulativebody extends over the distal electrode assembly to the contact electrodesuch that the contact electrode is exposed at the distal end of themedical device lead.

In Example 3, the medical device lead according to either Example 1 or2, wherein the coiled element comprises a unifilar coil.

In Example 4, the medical device lead according to any of Examples 1-3,wherein a resistance of the coiled element is less than about 100 ohms.

In Example 5, the medical device lead according to any of Examples 1-4,and further comprising a fixation helix disposed within the distalelectrode assembly and configured to extend from and retract into adistal end of the distal electrode assembly.

In Example 6, the medical device lead according to any of Examples 1-5,and further comprising an insulative layer configured to electricallyisolate the fixation helix from the distal electrode assembly.

In Example 7, the medical device lead according to any of Examples 1-6,and further comprising a coupler disposed within the distal electrodeassembly and fixedly attached to the fixation helix, wherein the coupleris rotatable with respect to the distal electrode assembly to translatethe fixation helix longitudinally with respect to the distal electrodeassembly.

In Example 8, the medical device lead according to any of Examples 1-7,wherein the coupler includes a slot configured to receive a distal endof an actuating device to rotate the coupler.

In Example 9, a distal electrode assembly for an implantable medicaldevice includes a proximal portion configured for electrical connectionto a conductive coil that delivers electrical energy to the distalelectrode assembly, a distal portion including a contact electrode, andan intermediate portion comprising a coiled element electricallyconnecting the proximal portion to the distal portion.

In Example 10, the distal electrode assembly according to Example 9,wherein the coiled element comprises a unifilar coil.

In Example 11, the distal electrode assembly according to either Example9 or 10, wherein the unifilar coil has a filar diameter of 0.002-0.007inch (0.051-0.178 mm).

In Example 12, the distal electrode assembly according to any ofExamples 9-11, wherein a resistance of the coiled element is less thanabout 100 ohms.

In Example 13, the distal electrode assembly according to any ofExamples 9-12, and further comprising a fixation helix disposed withinthe distal electrode assembly and configured to extend from and retractinto a distal end of the distal electrode assembly.

In Example 14, the distal electrode assembly according to any ofExamples 9-13, and further comprising an insulative layer configured toelectrically isolate the fixation helix from the distal electrodeassembly.

In Example 15, a medical device lead includes an insulative body havinga proximal region with a proximal end, and a distal region with a distalend. The medical device lead also includes a conductive coil extendingthrough the insulative body, and a distal electrode assembly at a distalend of the insulative body. The distal electrode assembly includes aproximal portion electrically coupled to a distal end of the conductor,a distal portion, and an intermediate portion. The intermediate portioncomprises a coiled element electrically connecting the proximal portionand distal portion. The coiled element comprises a unifilar coil havinga pitch of less than two.

In Example 16, the medical device lead according to Example 15, andfurther comprising a fixation helix disposed within the distal electrodeassembly and configured to extend from and retract into a distal end ofthe distal electrode assembly.

In Example 17, the medical device lead according to either Example 15 or16, wherein the distal portion of the distal electrode assembly includesa contact electrode having an outer diameter larger than outer diametersof the proximal portion and intermediate portion, and wherein theinsulative body extends over the distal electrode assembly to thecontact electrode such that the contact electrode is exposed at thedistal end of the medical device lead.

In Example 18, the medical device lead according to any of Examples15-17, and further comprising a fixation helix disposed within thedistal electrode assembly and configured to extend from and retract intoa distal end of the distal electrode assembly.

In Example 19, the medical device lead according to any of Examples15-18, and further comprising an insulative layer configured toelectrically isolate the fixation helix from the distal electrodeassembly.

In Example 20, the medical device lead according to any of Examples15-19, and further comprising a coupler disposed within the distalelectrode assembly and fixedly attached to the fixation helix, whereinthe coupler is rotatable with respect to the distal electrode assemblyto translate the fixation helix longitudinally with respect to thedistal electrode assembly, and wherein the coupler includes a slotconfigured to receive a distal end of an actuating device to rotate thecoupler.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a combined cutaway of a heart and a perspective view of animplantable medical device and lead in accordance with one embodiment.

FIG. 2 is a side view of an embodiment of a lead as shown in FIG. 1.

FIG. 3A is a sectioned side view of an embodiment of a distal end of alead, including an electrode with a coiled portion.

FIG. 3B is a side view of the distal end of the lead shown in FIG. 3A.

FIG. 4A is a sectioned side view of an embodiment of an electrodeportion of a lead, including an insulative layer between the electrodehousing and fixation helix.

FIG. 4B is an exploded side view of the electrode portion shown in FIG.4A.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of an implantable medical device (IMD) 10in accordance with one embodiment. The IMD 10 includes a pulse generator12 and a cardiac lead 14. The lead 14 operates to convey electricalsignals between the heart 16 and the pulse generator 12. The lead 14 hasa proximal region 18 and a distal region 20. The lead 14 includes a leadbody, or flexible body 22, extending from the proximal region 18 to thedistal region 20. The proximal region 18 is coupled to the pulsegenerator 12 and the distal region 20 is coupled to the heart 16. Thedistal region 20 includes an extendable/retractable fixation helix 24,which will be discussed in greater detail with respect to subsequentdrawings, and which locates and/or secures the distal region 20 withinthe heart 16. In one alternative embodiment, the distal region 20includes a plurality of tines or other structures for fixation of thelead 14 relative to the heart 20 (e.g., in a coronary vein orventricular trabeculae).

The distal region 20 of the lead 14 has an axially compact design thataccommodates a dedicated bipolar electrode configuration. The lead 14may alternatively have other electrode configurations. As will beexplained in further detail herein and shown in additional figures, thedistal region 20 includes an electrically conductive electrode housingwith a hollow interior that accommodates an extendible/retractablefixation helix 24. In some embodiments, the electrode housing includes alength having a coiled component that connects proximal and distalportions of the electrode housing. In some embodiments, the electrodehousing is electrically isolated from the fixation helix 24, such aswith an insulative layer between the electrode housing and fixationhelix 24.

The pulse generator 12 typically includes a connector header 13 thatcouples the pulse generator 12 to the lead 14. The connector header 13typically contains one or more bores 17 that is/are able to receive aconnector (not shown) that is part of a connector assembly (not shown,but see 40 in FIG. 2, discussed herein) formed near the proximal region18 of the lead 14, wherein electrical contacts (not shown) of theconnector header 13 couple with lead contacts (not shown) of theconnector assembly (not shown).

The connector header 13 can be attached to a hermetically sealedenclosure 15 that contains a battery, electronic circuitry, and othercomponents known to those skilled in the art. Electrical contacts (notshown) in the connector header 13 can be a type known to those skilledin the art that are electrically connected via feedthroughs (not shown)mounted to extend through the hermetically sealed enclosure 15 in orderto electrically couple the lead 14 with pulse generator 12.

The pulse generator 12 can be implanted subcutaneously within animplantation location or pocket in the patient's chest or abdomen. Inembodiments in which the lead 14 is a neural lead, the pulse generatormay alternatively be implanted at the patient's back or buttocks. Thepulse generator 12 may be any implantable medical device known in theart or later developed, for delivering an electrical therapeuticstimulus to the patient. In various embodiments, the pulse generator 12is a pacemaker, an implantable cardioverter/defibrillator (ICD), acardiac resynchronization (CRT) device configured for bi-ventricularpacing, and/or includes combinations of pacing, CRT, and defibrillationcapabilities.

The lead body 22 can be made from a flexible, biocompatible materialsuitable for lead construction. In various embodiments, the lead body 22is made from a flexible, electrically insulative material. In oneembodiment, the lead body 22 is made from silicone rubber. In anotherembodiment, the lead body 22 is made from polyurethane. In variousembodiments, respective segments of the lead body 22 are made fromdifferent materials, so as to tailor the lead body 22 characteristics toits intended clinical and operating environments. In variousembodiments, proximal and distal ends of the lead body 22 are made fromdifferent materials selected to provide desired functionalities.

The heart 16 includes a right atrium 26, a right ventricle 28, a leftatrium 30 and a left ventricle 32. The heart 16 includes an endothelialinner lining or endocardium 34 covering the myocardium 36. In someembodiments as illustrated, the fixation helix 24, located at the distalregion 20 of the lead, penetrates through the endocardium 34, and isimbedded within the myocardium 36. Alternatively, the lead 14 may beconfigured as a passive fixation lead as discussed herein. In oneembodiment, the IMD 10 includes a plurality of leads 14. For example, itmay include a first lead 14 adapted to convey electrical signals betweenthe pulse generator 12 and the right ventricle 28, and a second lead(not shown) adapted to convey electrical signals between the pulsegenerator 12 and the right atrium 26. Additional leads may also beemployed. For example, in various embodiments, a coronary venous lead(not shown) may be utilized for stimulating a left atrium 30 and/or aleft ventricle 32 of the heart 16.

In the illustrated embodiment shown in FIG. 1, the fixation helix 24penetrates the endocardium 34 of the right ventricle 28 and is imbeddedin the myocardium 36 of the heart 16. In some embodiments, the fixationhelix 24 is electrically active and thus can be used to sense theelectrical activity of the heart 16 or to apply a stimulating pulse tothe right ventricle 28. In other embodiments, the fixation helix 24 isnot electrically active. In still other embodiments, the lead 14 isfixed relative to the heart 16 using passive structures (e.g., tines,spirals, etc.).

During operation, the lead 14 can be configured to convey electricalsignals between the IMD 12 and the heart 16. For example, in thoseembodiments in which the IMD 12 is a pacemaker, the lead 14 can beutilized to deliver electrical stimuli for pacing the heart 16. In thoseembodiments in which the IMD 12 is an implantable cardiac defibrillator,the lead 14 can be utilized to deliver electric shocks to the heart 16in response to an event such as a heart attack or arrhythmia. In someembodiments, the IMD 12 includes both pacing and defibrillationcapabilities.

The electrical signals are carried between the IMD 12 and electrodes atthe distal region 20 by one or more conductors extending through thelead 14. The one or more conductors are electrically coupled to aconnector suitable for interfacing with the IMD 12 at the proximalregion 18 of the lead 14 and to the one or more electrodes at the distalregion 20. According to various embodiments, the one or more conductorsinclude at least one composite conductor comprising a multiconductorwire. In some embodiments, the multiconductor wires are configured todeliver low voltage signals to the one or more electrodes.

FIG. 2 is an isometric illustration of a lead 14 according to someembodiments. A connector assembly 40 is disposed at or near the proximalregion 18, or proximal end, of the lead 14. The connector assembly 40includes a connector 42 and a terminal pin 44. The connector 42 isconfigured to be coupled to the lead body 22 and is configured tomechanically and electrically couple the lead 14 to the header 13 on thepulse generator 12 (see FIG. 1). In some embodiments, the terminal pin44 includes an aperture (not shown) extending therethrough in order toaccommodate a guide wire or an insertion stylet. For example, in someembodiments, a clinician may use a stylet inserted through the terminalpin 44 in the proximal region 40 to actuate the fixation helix 42 in thedistal region 46. In alternative embodiments, the terminal pin 44extends proximally from the connector 42 and in some embodiments iscoupled to a conductor member (not visible in this view) that extendslongitudinally through the lead body 22 such that rotating the terminalpin 44 relative to the lead body 22 causes the conductor member torotate within the lead body 22.

A distal assembly 46 is disposed at or near the distal region 20 ordistal end of the lead 14 or lead body 22. Depending on the functionalrequirements of the IMD 10 (see FIG. 1) and the therapeutic needs of apatient, the distal region 20 of the lead 14 may include one or moreelectrodes. In the illustrated embodiment, the distal region 20 includesone or more coil electrodes 48 and 49 that can function as shockingelectrodes for providing, for example, a defibrillation shock to theheart 16. In some embodiments, the coil electrodes 48 and 49 include acoating that is configured to control (i.e., promote or discourage)tissue ingrowth. In various embodiments, the lead 14 may include only asingle coil electrode. In various other embodiments, the lead 14 alsoincludes one or more low-voltage electrodes (e.g., ring electrodes),such as electrode 47, along the lead body 22 in lieu of or in additionto the coil electrodes 48, 49. When present, the low-voltage electrodesoperate as relatively low-voltage, pace/sense electrodes. As will beappreciated by those skilled in the art, a wide range of electrodecombinations may be incorporated into the lead 14 within the scope ofthe various embodiments.

The distal assembly 46 includes a distal electrode assembly 50, withinwhich the fixation helix 24, or helical electrode, is at least partiallydisposed. As will be explained in greater detail herein, the distalelectrode assembly 50 accommodates a mechanism that enables the fixationhelix 24 to move distally and proximally relative to the distalelectrode assembly 50, but that includes structure (not seen in thisview) that limits distal travel of the fixation helix 24 (relative tothe distal electrode assembly 50) in order to reduce or preventover-extension of the fixation helix 24. In some embodiments, the distalend of the distal electrode assembly 50 is electrically active toprovide electrical signals at the surface of the endocardial tissue. Asnoted herein, the fixation helix 24 operates as an anchoring means foranchoring the distal region 20 of the lead 14 within the heart 16. Inalternative embodiments, the lead 14 is fixed relative to the heart 16using passive structures (e.g., tines, spirals, etc.).

In some embodiments, the fixation helix 24, or helical electrode, iselectrically active, and is used as a low-voltage, pace/sense electrode.In some embodiments, the fixation helix 24 is made of an electricallyconductive material such as ELGILOY™, MP35N™, tungsten, tantalum,iridium, platinum, titanium, palladium, stainless steel as well asalloys of these materials. In alternative embodiments, the fixationhelix 24 is electrically inactive and/or electrically isolated from thehousing 50 with an insulative layer. For example, the fixation helix 24could be made from a non-conductive material such as a polymer orceramic.

The lead 14 is one exemplary implementation of a lead in accordance withthe present disclosure, and other configurations for the lead 14 arealso possible. For example, while coil electrodes 48, 49 are shownadjacent to each other, the coil electrode 49 may alternatively bedisposed more proximally on the lead 14. As another example, the lead 14may include a plurality of annular electrodes along the distal region 20for providing pacing and/or sensing signals to adjacent tissue.

FIG. 3A is a sectioned side view, and FIG. 3B is a side view of anembodiment of the distal region 46 of the lead 14 including distalelectrode assembly 50. In FIG. 3B, the lead body 22 is removed to betterillustrate the features of the distal electrode assembly 50. The distalelectrode assembly 50 includes a proximal portion 60, an intermediateportion 62, and a distal portion 64. The intermediate portion 62mechanically and electrically couples the proximal portion 60 to thedistal portion 64.

The proximal portion 60 is configured for coupling with a distal end ofa coil conductor 66 extending through the lead body 22. In someembodiments, a proximal end of the coil conductor 66 (not shown) isconnected to the connector assembly 40 at the proximal region 18 of thelead 14. In the embodiment shown, the coil conductor 66 couples with aconductor coupling region 68 of the proximal portion 60. For example,the proximal portion 60 may include a helical groove 69 that is sizedand shaped to receive the distal end of the coil conductor 66, such thatthe coil conductor 66 is secured with respect to the proximal portion60. The connection of the proximal portion 60 with the distal end of thecoil conductor 66 thus electrically connects the electrode assembly 50with the connector assembly 40. In some embodiments, the pitch of thecoil conductor 66 is increased at the distal end of the coil conductor66 to allow the coil conductor 66 to couple with the proximal portion60. In some embodiments, the coil conductor 66 comprises one or moreinsulated filars that are stripped of insulation at the distal end ofthe coil conductor 66 to allow electrical contact between the coilconductor 66 and proximal portion 60.

The distal portion 64 is disposed at the distal end of the lead 14 andis electrically coupled to the proximal portion 60 via the intermediateportion 62. In some embodiments, the distal portion 64 includes a distalcontact electrode 70 that has an outer diameter D₁ that is greater thanthe outer diameter D₂ of the proximal portion 60 and intermediateportion 62. The contact electrode 70 is configured to contact anddeliver electrical energy to endocardial tissue when the lead 14 isimplanted. In some embodiments, the lead body 22 extends over theproximal portion 60, intermediate portion 62, and parts of the distalportion 64 to the contact electrode 70. That is, the contact electrode70 remains exposed in the assembled lead 14, while the remainingportions of the electrode assembly 50 are covered by the lead body 22.

The proximal portion 60 may be comprised of the same or similar materialas the distal portion 64. The proximal portion 60 and distal portion 64may include precious metals such as gold, silver, or platinum. Exemplarymaterials for the proximal portion 60 and distal portion 64 alsoinclude, but are not limited to, MPAg (MP35N with silver), MPTa (MP35Nwith tantalum), platinum-clad Ta, platinum-clad MP35N, MP35N, Nitinol,and palladium.

The intermediate portion 62 comprises a coiled element 72 that extendsfrom the proximal portion 60 to the distal portion 64. The coiledelement 72 includes one or more filars wound into a coil having an outerdiameter substantially the same as adjacent sections of the proximalportion 60 and distal portion 64. As discussed herein, the coiledelement 72 is electrically and mechanically connected to the proximalportion 60 and distal portion 64. In some embodiments, the coiledelement 72 is connected to the proximal portion 60 and distal portion 64by welding, swaging, or crimping the proximal and distal ends of thecoiled element 72 to the proximal portion 60 and distal portion 64,respectively. In some embodiments, the coiled element 72 is covered(e.g., overmolded) with a polymeric material to improve the durabilityof the coiled element 72, provide suitable corrosion performance, andmaintain the pitch and shape of the coiled element.

The coiled element 72 may have an outer diameter D₂ of less than about0.1 inch (2.54 millimeter (mm)). For example, in some exemplaryimplementations, the outer diameter D₂ of the coiled element 72 is inthe range of about 0.03 inch to about 0.1 inch (0.762-2.54 mm). In someembodiments, the coiled element 72 consists of a single filar ofconductive material (i.e., unifilar) that is helically coiled with aplurality of co-radial turns. The turns of the coiled element 72 may beclosely wound. For example, in some embodiments, the coiled element 72has a pitch of between about one and two times the filar diameter. Inthe illustrated embodiment, the coiled element 72 has a pitchapproximately equal to the filar diameter (i.e., the turns of the coiledelement 72 abut each other). The pitch may be consistent along thelength of the coiled element 72, or may be varied along at least aportion of the coiled element 72. One exemplary approach toincorporating variable pitch sections into the coiled element 72 isdescribed in U.S. Patent App. Pub. No. 2009/0149933, entitled“Implantable Lead Having a Variable Coil Conductor Pitch,” which ishereby incorporated by reference in its entirety. The direction of thepitch of the coiled element 72 may also be a function of the windingdirection of other coiled elements (e.g., coil conductor 66). Forexample, in some embodiments, the coiled element 72 is wound in adirection opposite the coil conductor 66.

In some embodiments, the filar of the coiled element 72 has a diameterof between about 0.001 inch and 0.007 inch (0.025-0.178 mm). Oneexemplary material suitable for the coiled element 72 is MP35N includinga silver core (e.g., 25% to 50% silver). Other exemplary materialssuitable for the coiled element 72 include, but are not limited to, MPTa(MP35N with tantalum), platinum-clad Ta, platinum-clad MP35N, MP35N,Nitinol, and palladium. In some embodiments, the filar of the coiledelement 72 is insulated. In some embodiments, the coiled element 72 isconfigured to have a resistance of less than about 100 ohms (Ω).

The inclusion of a coiled element 72 in the electrode assembly 50provides several advantages over solid electrode assemblies. Forexample, as discussed above, the proximal and distal portions 60, 64 maybe comprised of precious metals. By using a coiled element 72 to connectthe proximal portion 60 to the distal portion 64, less precious metal isused to fabricate the electrode assembly 50 versus an electrode assemblymade of a solid length of material. Consequently, the overall cost tomanufacture the lead 14 is reduced. At the same time, the coiled element72 also generates fewer image artifacts in images generated usingmagnetic resonance imaging (MRI) while providing good radiopacity todiscern the location of the electrode assembly 50 during imaging, sinceprecious metals have a density that images well under the types ofvision systems employed during implantation.

In addition, exposure of the lead 14 to MRI fields can result inlocalized heating of the contact electrode 70 due to excitation of thelead conductors (e.g., coil conductor 66). Conductors with highinductance (>1 pH) are more resistant to excitation in MRI fields. Theinductance of the conductor is determined by its geometric properties,including whether the conductor is straight or coiled. For a coiled orwound conductor, such as the coiled element 72, several parametersinfluence its inductance, including the coil pitch, the outer diameterof the coiled element 72, the cross-sectional area of the coiled element72, and the number of filars comprising the coiled element 72. Forexample, in some embodiments, the coil pitch (i.e., the distance betweenthe centers of adjacent coil turns) may be small (e.g., one to two timesthe cable filar diameter). The coiled element 72 is shown having a pitchapproximately equal to the filar diameter in FIGS. 3A and 3B (that is,turns of the coil are adjacent to each other). The pitch direction mayalso be selected (e.g., in the opposite direction as the coil conductor66) to control heating of the electrode assembly 50 under MRIconditions. Thus, the dimensions and characteristics of the coil 52 maybe selected to minimize the effects of magnetic resonance imaging (MRI)fields on the performance and response of the lead 14.

The fixation helix 24 may be disposed within a hollow interior of theelectrode assembly 50. In some embodiments, the fixation helix 24 is atube of conductive material laser cut or Swiss cut into a helical shape.A coupler 76 may be fixedly coupled to a proximal end of the fixationhelix 24 to facilitate actuation of the fixation helix 24. In someembodiments, the coupler 76 may include a slot 78 that is accessible viaan inner lumen 80 of the lead 14 with a stylet. For example, the styletmay be a bladed tip stylet having a distal feature sized and shaped tomate with the slot 78. To actuate the fixation helix 24, the stylet ispushed through the lumen 80 from the proximal region 18 of the lead 14until the distal end of the stylet interfaces with the slot 78 in thecoupler 76. The stylet is then rotated to rotate the fixation helix 24,which results in longitudinal movement of the fixation helix 24 relativeto the lead 14. This allows the distal tip of the fixation helix 24 tobe advanced into tissue during implantation, or retracted back into theelectrode assembly 50.

In an alternative embodiment, the fixation helix 24 includes a torquetube 81 that is mechanically coupled to the fixation helix 24 (e.g., viathe coupler 76). The torque tube 81 may be mechanically coupled to theterminal pin 44 on the connector assembly 40 to allow rotation andadvancement of the fixation helix 24 by rotating the terminal pin 44.That is, the torque on the terminal pin 44 is transmitted to thefixation helix 24 via the torque tube 81. In some embodiments, thetorque tube 81 is comprised of one or more polymeric fibers that arecovered by an insulative coating or sheath. In some embodiments, thelumen 80 of the torque tube 81 comprises a smooth surface to facilitateinsertion of a stylet or guide wire.

The electrode assembly 50 may also include a peg 82 against which turnsof the fixation helix 24 rotate to maintain axial stability duringactuation of the fixation helix 24. The peg 82 enables the fixationhelix 24 to move distally and proximally relative to the electrodeassembly 50, but limits distal travel of the fixation helix 24 (relativeto the distal electrode assembly 50) in order to reduce or preventover-extension of the fixation helix 24. The peg 82 may be made of apolymeric material, for example.

In alternative embodiments, the lead 14 may be fixated using passivefixation structures (e.g., tines) disposed on an exterior surface of thedistal region 46, and/or a drug eluting element may be disposed in thehollow interior of the electrode assembly 50 in lieu of the fixationhelix 24.

FIG. 4A is a sectioned side view, and FIG. 4B is an exploded side view,of another embodiment of an electrode assembly 50 of the lead 14. Theelectrode assembly includes an outer conductive shell 90, an insulativelayer 92, and a fixation helix 24. The electrode assembly 50 alsoincludes a coupler 76 and a peg 82 having functionality similar to theembodiment illustrated in FIGS. 3A and 3B. The proximal end of theelectrode assembly 50 also includes a helical groove 69 sized and shapedto couple with a conductive coil, similar to the embodiment illustratedin FIGS. 3A and 3B. Additionally, the conductive housing 90 includes acontact electrode 70 at the distal end of the conductive housing 90. Insome embodiments, in the assembled lead 14 the lead body 22 is disposedover the portions of the conductive housing 90 up to the contactelectrode 70, thereby leaving only the contact electrode 70 exposed atthe distal end of the lead 14. While the electrode assembly 50 includesan outer conductive shell 90 comprised of a solid length of conductivematerial in the embodiment illustrated in FIGS. 4A and 4B, the electrodeassembly 50 may alternatively be configured to include a coiled element72 as described herein.

The insulative layer 92 is disposed between the outer conductive shell90 and the fixation helix 24. In some embodiments, the insulative layer92 electrically isolates the fixation helix 24 from the outer conductiveshell 90. The insulative layer 92 may also be configured such that thefixation helix 24 is electrically inactive, and operates only as afixation mechanism. The insulative layer 92 may be comprised of amaterial including, but not limited to, high durometer polyurethanes,hybrid high durometer polymers, ceramic, and epoxies, PEEK, ETFE, PTFEand derivatives, and/or parylene C. In some embodiments, the insulativelayer 92 is formed on a metal substrate.

In this configuration, the tissue to be stimulated by the outerconductive shell 90 is distanced from the tissue attached to thefixation helix 24 for anchoring the lead 14. The tissue surrounding thefixation helix 24 may be agitated or going through the healing processand, as a result, may have a higher chronic threshold than othersurrounding tissue. Consequently, by electrically isolating the fixationhelix 24 from the outer conductive shell 90, the likelihood ofelectrical stimulation being delivered to tissue having a lower chronicthreshold is increased.

The conductive housing 90 may be used in association with mappingsystems to locate the distal region 46 of the lead 14 and/or facilitatedevelopment of a two- or three-dimensional representation of the heart16 or one or more chambers of the heart 16. For example, the conductivehousing 90 may be employed for establishing relative location andorientation of the lead 14 with respect to a mapping catheter located inanother portion of the heart 16.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

I claim:
 1. A medical device lead comprising: an insulative body havinga proximal region with a proximal end, and a distal region with a distalend; a connector coupled to the proximal end of the insulative body ofthe lead configured to electrically and mechanically connect the lead toan implantable pulse generator; a conductor extending through theinsulative body, a proximal end of the conductor electrically connectedto the connector; and a distal electrode assembly at a distal end of theinsulative body, the distal electrode assembly including a proximalportion electrically coupled to a distal end of the conductor, a distalportion, and an intermediate portion, wherein the intermediate portioncomprises a coiled element electrically connecting the proximal portionand distal portion.
 2. The medical device lead of claim 1, wherein thedistal portion of the distal electrode assembly includes a contactelectrode having an outer diameter larger than outer diameters of theproximal portion and intermediate portion, and wherein the insulativebody extends over the distal electrode assembly to the contact electrodesuch that the contact electrode is exposed at the distal end of themedical device lead.
 3. The medical device lead of claim 1, wherein thecoiled element comprises a unifilar coil.
 4. The medical device lead ofclaim 1, wherein a resistance of the coiled element is less than about100 ohms.
 5. The medical device lead of claim 1, and further comprising:a fixation helix disposed within the distal electrode assembly andconfigured to extend from and retract into a distal end of the distalelectrode assembly.
 6. The medical device lead of claim 5, and furthercomprising: an insulative layer configured to electrically isolate thefixation helix from the distal electrode assembly.
 7. The medical devicelead of claim 5, and further comprising: a coupler disposed within thedistal electrode assembly and fixedly attached to the fixation helix,wherein the coupler is rotatable with respect to the distal electrodeassembly to translate the fixation helix longitudinally with respect tothe distal electrode assembly.
 8. The medical device lead of claim 7,wherein the coupler includes a slot configured to receive a distal endof an actuating device to rotate the coupler.
 9. A distal electrodeassembly for an implantable medical device, the distal electrodeassembly comprising: a proximal portion configured for electricalconnection to a conductive coil that delivers electrical energy to thedistal electrode assembly; a distal portion including a contactelectrode; and an intermediate portion electrically connecting theproximal portion to the distal portion, wherein the intermediate portioncomprises a coiled element.
 10. The distal electrode assembly of claim9, wherein the coiled element comprises a unifilar coil.
 11. The distalelectrode assembly of claim 9, wherein the unifilar coil has a filardiameter of 0.001-0.007 inch (0.025-0.178 mm).
 12. The distal electrodeassembly of claim 9, wherein a resistance of the coiled element is lessthan about 100 ohms.
 13. The distal electrode assembly of claim 9, andfurther comprising: a fixation helix disposed within the distalelectrode assembly and configured to extend from and retract into adistal end of the distal electrode assembly.
 14. The distal electrodeassembly of claim 13, and further comprising: an insulative layerconfigured to electrically isolate the fixation helix from the distalelectrode assembly.
 15. A medical device lead comprising: an insulativebody having a proximal region with a proximal end, and a distal regionwith a distal end; a conductive coil extending through the insulativebody; and a distal electrode assembly at a distal end of the insulativebody, the distal electrode assembly including a proximal portionelectrically coupled to a distal end of the conductor, a distal portion,and an intermediate portion, wherein the intermediate portion comprisesa coiled element electrically connecting the proximal portion and distalportion, and wherein the coiled element comprises a unifilar coil havinga pitch of less than two.
 16. The medical device lead of claim 15, andfurther comprising: a fixation helix disposed within the distalelectrode assembly and configured to extend from and retract into adistal end of the distal electrode assembly.
 17. The medical device leadof claim 16, wherein the distal portion of the distal electrode assemblyincludes a contact electrode having an outer diameter larger than outerdiameters of the proximal portion and intermediate portion, and whereinthe insulative body extends over the distal electrode assembly to thecontact electrode such that the contact electrode is exposed at thedistal end of the medical device lead.
 18. The medical device lead ofclaim 16, and further comprising: a fixation helix disposed within thedistal electrode assembly and configured to extend from and retract intoa distal end of the distal electrode assembly.
 19. The medical devicelead of claim 18, and further comprising: an insulative layer configuredto electrically isolate the fixation helix from the distal electrodeassembly.
 20. The medical device lead of claim 19, and furthercomprising: a coupler disposed within the distal electrode assembly andfixedly attached to the fixation helix, wherein the coupler is rotatablewith respect to the distal electrode assembly to translate the fixationhelix longitudinally with respect to the distal electrode assembly, andwherein the coupler includes a slot configured to receive a distal endof an actuating device to rotate the coupler.